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Anharmonicity and confinement in zeolites: structure, spectroscopy, and adsorption free energy of ethanol in H-ZSM-5

Konstantinos Alexopoulos, M-S Lee, Y Liu, Y Zhi, YS Liu, Marie-Françoise Reyniers UGent, Guy Marin UGent, V-A Glezakou, R Rousseau and J Lercher (2016) JOURNAL OF PHYSICAL CHEMISTRY C. 120(13). p.7172-7182
abstract
To account for thermal and entropic effects caused by the dynamics of the motion of the reaction intermediates, ethanol adsorption on the Bronsted acid site of the H-ZSM-5 catalyst has been studied at different temperatures and ethanol loadings using ab initio molecular dynamics (AIMD) simulations, infrared (IR) spectroscopy, and calorimetric measurements. At low temperatures (T <= 400 K) and ethanol loading, a single ethanol molecule adsorbed in H-ZSM-5 forms a Zundel-like structure where the proton is equally shared between the oxygen of the zeolite and the oxygen of the alcohol. At higher ethanol loading, a second ethanol molecule helps to stabilize the protonated ethanol at all temperatures by acting as a solvating agent. The vibrational density of states (VDOS), as calculated from the AIMD simulations, are in excellent agreement with measured IR spectra for C2H5OH, C2H5OD, and C2D5OH isotopomers and support the existence of both monomers and dimers. A quasi-harmonic approximation (QHA), applied to the VDOS obtained from the AIMD simulations, provides estimates of adsorption free energy within similar to 10 kJ/mol of the experimentally determined quantities, whereas the traditional approach, employing harmonic frequencies from a single ground state minimum, strongly overestimates the adsorption free energy by at least 20 similar to 50 kJ/mol. This discrepancy is traced back to the inability of the harmonic approximation to represent the contributions to the vibrational motions of the ethanol molecule upon confinement in the zeolite.
Please use this url to cite or link to this publication:
author
organization
year
type
journalArticle (original)
publication status
published
subject
keyword
NITRILE ADSORPTION, AB-INITIO, PROTON-TRANSFER, ACID CATALYSIS, ALKANES, COMPLEXES, METHANOL, ALCOHOL, PSEUDOPOTENTIALS, DEHYDRATION
journal title
JOURNAL OF PHYSICAL CHEMISTRY C
volume
120
issue
13
pages
7172 - 7182
Web of Science type
Article
Web of Science id
000373862700030
JCR category
MATERIALS SCIENCE, MULTIDISCIPLINARY
JCR impact factor
4.536 (2016)
JCR rank
43/275 (2016)
JCR quartile
1 (2016)
ISSN
1932-7447
DOI
10.1021/acs.jpcc.6b00923
language
English
UGent publication?
yes
classification
A1
copyright statement
I have transferred the copyright for this publication to the publisher
id
8055128
handle
http://hdl.handle.net/1854/LU-8055128
date created
2016-08-25 15:15:44
date last changed
2017-03-09 12:54:27
@article{8055128,
  abstract     = {To account for thermal and entropic effects caused by the dynamics of the motion of the reaction intermediates, ethanol adsorption on the Bronsted acid site of the H-ZSM-5 catalyst has been studied at different temperatures and ethanol loadings using ab initio molecular dynamics (AIMD) simulations, infrared (IR) spectroscopy, and calorimetric measurements. At low temperatures (T {\textlangle}= 400 K) and ethanol loading, a single ethanol molecule adsorbed in H-ZSM-5 forms a Zundel-like structure where the proton is equally shared between the oxygen of the zeolite and the oxygen of the alcohol. At higher ethanol loading, a second ethanol molecule helps to stabilize the protonated ethanol at all temperatures by acting as a solvating agent. The vibrational density of states (VDOS), as calculated from the AIMD simulations, are in excellent agreement with measured IR spectra for C2H5OH, C2H5OD, and C2D5OH isotopomers and support the existence of both monomers and dimers. A quasi-harmonic approximation (QHA), applied to the VDOS obtained from the AIMD simulations, provides estimates of adsorption free energy within similar to 10 kJ/mol of the experimentally determined quantities, whereas the traditional approach, employing harmonic frequencies from a single ground state minimum, strongly overestimates the adsorption free energy by at least 20 similar to 50 kJ/mol. This discrepancy is traced back to the inability of the harmonic approximation to represent the contributions to the vibrational motions of the ethanol molecule upon confinement in the zeolite.},
  author       = {Alexopoulos, Konstantinos and Lee, M-S and Liu, Y and Zhi, Y and Liu, YS and Reyniers, Marie-Fran\c{c}oise and Marin, Guy and Glezakou, V-A and Rousseau, R and Lercher, J},
  issn         = {1932-7447},
  journal      = {JOURNAL OF PHYSICAL CHEMISTRY C},
  keyword      = {NITRILE ADSORPTION,AB-INITIO,PROTON-TRANSFER,ACID CATALYSIS,ALKANES,COMPLEXES,METHANOL,ALCOHOL,PSEUDOPOTENTIALS,DEHYDRATION},
  language     = {eng},
  number       = {13},
  pages        = {7172--7182},
  title        = {Anharmonicity and confinement in zeolites: structure, spectroscopy, and adsorption free energy of ethanol in H-ZSM-5},
  url          = {http://dx.doi.org/10.1021/acs.jpcc.6b00923},
  volume       = {120},
  year         = {2016},
}

Chicago
Alexopoulos, Konstantinos, M-S Lee, Y Liu, Y Zhi, YS Liu, Marie-Françoise Reyniers, Guy Marin, V-A Glezakou, R Rousseau, and J Lercher. 2016. “Anharmonicity and Confinement in Zeolites: Structure, Spectroscopy, and Adsorption Free Energy of Ethanol in H-ZSM-5.” Journal of Physical Chemistry C 120 (13): 7172–7182.
APA
Alexopoulos, K., Lee, M.-S., Liu, Y., Zhi, Y., Liu, Y., Reyniers, M.-F., Marin, G., et al. (2016). Anharmonicity and confinement in zeolites: structure, spectroscopy, and adsorption free energy of ethanol in H-ZSM-5. JOURNAL OF PHYSICAL CHEMISTRY C, 120(13), 7172–7182.
Vancouver
1.
Alexopoulos K, Lee M-S, Liu Y, Zhi Y, Liu Y, Reyniers M-F, et al. Anharmonicity and confinement in zeolites: structure, spectroscopy, and adsorption free energy of ethanol in H-ZSM-5. JOURNAL OF PHYSICAL CHEMISTRY C. 2016;120(13):7172–82.
MLA
Alexopoulos, Konstantinos, M-S Lee, Y Liu, et al. “Anharmonicity and Confinement in Zeolites: Structure, Spectroscopy, and Adsorption Free Energy of Ethanol in H-ZSM-5.” JOURNAL OF PHYSICAL CHEMISTRY C 120.13 (2016): 7172–7182. Print.